// Problem: 
// Contest: 
// URL: 
// Memory Limit: 
// Time Limit: 
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize("unroll-loops")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#include<bits/stdc++.h>
using namespace std;
#define int long long
inline int read(){
	int s=0,w=1;
	char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')w=-1;ch=getchar();}
	while(ch>='0'&&ch<='9') s=s*10+ch-'0',ch=getchar();
	return s*w;
}
struct po
{
	int x,y,z;
};
bool cmp(po x,po y)
{
	if(x.z<y.z)return 1;
	return 0;
}
signed main()
{
	int n;
	cin>>n;
	po p[n];
	for(int i=0;i<n;i++)
	{
		cin>>p[i].x>>p[i].y>>p[i].z;
	}
	sort(p,p+n,cmp);
	double ans;
	for(int i=0;i<n-1;i++)
	{
		int x0=p[i+1].x-p[i].x;
		int y0=p[i+1].y-p[i].y;
		int z0=p[i+1].z-p[i].z;
		ans+=sqrt(double(x0*x0+y0*y0+z0*z0));
	}
	printf("%0.3lf",ans);
	return 0;
}
